Sprayable cleaners have been used for many years for both household and institutional cleaning of a variety of organic and inorganic soils such as food residue, soap scum, grease, hardness components and the like. Commonly these cleaners comprise a major proportion of a solvent such as water or a mixed aqueous-organic solvent, and components such as chelating agents, including EDTA, NTA, and others; anionic, nonionic and cationic surfactants, disinfectants, fragrances and dyes. These spray cleaners are usually formulated at a near-neutral pH (about 7) up to an alkaline pH (up to about 12). These cleaners perform adequately on many soils, however in certain applications neutral or basic cleaners have had the drawback that certain soils, such as hardness components (calcium and magnesium salts precipitated from hard water) and soap scum (a precipitated calcium soap salt) can be very difficult to clean since these soils are less soluble at a basic pH. An acidic cleaner is indicated for soil removal in these instances.
However, acidic cleaners pose certain problems in use and formulation. Many surfactants are insoluble or will hydrolyze at an acid pH. Many fragrances are unstable at low pH. Although strong inorganic acids, such as hydrochloric or sulfuric acid readily attack basic soils, their use in water-based cleaning compositions can irritate or burn the user's skin and degrade metallic and painted surfaces. When sprayed, such cleaners can also create an acidic mist or fog which can cause eye irritation and damage, and if inhaled can cause nose and throat irritation and coughing. If inhaled in sufficient amounts such cleaners could result in lung damage. For these reasons, sprayable acidic cleaners have not drawn the attention that has been given to the development of sprayable neutral or basic cleaning compositions. However, a substantial need has arisen for an acidic cleaner which can be used to efficiently remove soils including mineral hardeners, soap scums, dirt, grease and body oil which are found in institutional and household bathrooms and kitchens.
Despite the advantages inherent in foamable acidic cleaning compositions, such as reduction of aerosol dispersion, high cling and visibility, etc., few have been disclosed to date, probably due to the fact that the strong acids thought to be necessary for effective cleansing power both destabilize foam and degrade the surfactants necessary to foam the composition.
Scherubel (U.S. Pat. No. 4,235,734) generally discloses that foamable cleaning compositions may be prepared employing acids, cationic or nonionic surfactants and an alkanol or inertly-substituted alkanol such as butyl carbitol. The alkanol is disclosed to stabilize the foam. The compositions disclosed in the Scherubel patent comprise solutions of the strong acid, hydrochloric acid, and a surfactant mixture primarily composed of a cationic "quat" surfactant.
Thus a need exists for an effective foamable cleaning composition comprising an aqueous solution of one or more weak acids and a compatible cleansing and foamforming solvent and surfactant system.